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  "body": "\n## Summary\n\nGraph theory is the part of [[combinatorics|0JKW7W7XFR]] that studies [[graphs|00C0BR7D7H]]: sets of vertices joined in pairs by edges.\nIt asks about paths and cycles, connectivity, colourings, matchings, embeddings in surfaces and the spectra of graph matrices.\nGraphs model networks of every kind, so the subject is central in computer science, operations research, chemistry and physics.\n\n## Explanations\n\n### L1 human\n\nA graph is a set of dots with lines between some pairs of dots.\nRoad maps, social networks and molecules can all be drawn this way.\nGraph theory asks questions such as: can one walk over every road exactly once and return home?\nEuler answered that question for the bridges of Königsberg in 1736, and this is often seen as the start of graph theory.\n",
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